Our work has suggested that insomniacs may have cognitive disorders by day, manifested by a decrease in semantic memory (the ability to retrieve or use material already well learned) and also suggested that cognitive processes during sleep may also be altered. The current study has pursued this possibility, by testing arousal thresholds to meaningless and meaningful stimuli during sleep, ability to respond to commands during sleep, and similar measures. We have found that although arousal thresholds differed significantly between sleep stages, there were no differences between insomniacs and normals. Insomniacs returned to sleep and stayed asleep between arousal tests with the same facility as controls, but believed that they had slept only half as long. There is further evidence, then, that insomniacs suffer from misperception of their state of consciousness.